a boy becomes a man through age.
Well, "man" and "boy" both have three letters, but you could also use "guy".
Boy Guy and Lad are also two of the probable answers.
Nino
Boy names that begin with the letter L:LanceLaneLarryLawrenceLeeLeifLeighLeoLeonLeonardLeroyLesLesterLewisLincolnLionelLloydLorenzoLucianLukeLymanLlywelynLewys
Dasher Dancer Donder (three of Santa's reindeer), delicious dinner dishes, drum (as a gift, "Little Drummer Boy," or "12 Drummers Drumming"), Deck the Halls, decorate, dominoes (gift), "Don we now our gay apparel"